The X-51A Waverider completed the final flight of its test program last week, which proved to be the longest air-breathing hypersonic flight ever.

The X-51A Waverider is an unmanned scramjet demonstration aircraft for hypersonic flight testing. Boeing developed the X-51 Waverider, and its first flight took place May 26, 2010. The idea of the program was to prove the viability of air-breathing, high-speed scramjet propulsion.

May 1 marked the fourth and final test flight of the X-51A Waverider. It took off from the Air Force Test Center at Edwards AFB, California a little after 10 a.m. It was coupled with the B-52H Stratofortress, and released at 50,000 feet.

The X-51A Waverider reached Mach 4.8 in 26 seconds while powered by a rocket booster, but after separation from the booster, it achieved Mach 5.1 at 60,000 feet.

Once the fuel supply was gone, the X-51A Waverider splashed into the Pacific Ocean. During its test flight, it traveled over 230 nautical miles in just over six minutes and collected 370 seconds of data.

"It was a full mission success," said Charlie Brink, X-51A program manager for the Air Force Research Laboratory Aerospace Systems Directorate. "I believe all we have learned from the X-51A Waverider will serve as the bedrock for future hypersonics research and ultimately the practical application of hypersonic flight."

@ Amiga500, what you contrast as necessary prerequisites for SCRAMJET use aligns quite nicely for a hypersonic cruise missile application to satisfy DoD's directive of prompt global strike ability with conventional weapons in as little as 1 hour. Maybe some learnings trickle into research for civilian applications years down the road, but x-51 has validated research and provided a viable path for a HSCM program.

But then, using something akin to Skylon to place a load of tungsten bolts in orbit means they will re-enter with extremely high Vmax, and with less time spent in hostile"air-space"... and won't be delicate enough to be destroyedat the first hint of SAM shrapnel.

DARPA/DoD have looked at orbiting tungsten rods for quickStrike before. Nothing ever came of it... possibly out of fear of "weaponising space", which would be pushing on a few treaties.